The Delft neutron reflectometer meets cold neutrons

The neutron reflectometer ROG at the TU Delft Reactor Institute now operates with neutrons from a hydrogen cold-source, which greatly improves the performance. In this paper we estimate the gain based on reflectometry geometry considerations, and present the experimentally realized changes due to moderation on the neutron spectrum. The experimentally obtained gain in flux over the spectrum varies from a factor 6.7 at 0.3 nm to a factor 65 at 1 nm. The neutron spectrum of the reflectometer shifted to higher wavelengths, with the peak now around 0.33 nm, which was around 0.17 nm before. This allows for measurements of the same momentum transfer range at larger angles. This, combined with the increase in intensity, results in a reduction of measurement time of a factor 20 to 90 depending on the measurement requirements. This significant change allows for example for time-resolved measurements, and/or for measurements with much smaller samples.